(a) Field of the Invention
The present invention relates to a battery charger, and more particularly to a charger designed for charging, discharging and supplying electric power to an AA or AAA rechargeable battery, and a manual switch synchronous control is provided to integrate a circuit structure with “an independent separate charging circuit and a combined serial discharging circuit.”
(b) Description of the Related Art
As portable 3C electronic products become more popular, the demand for batteries becomes higher as well. That a disposable battery (namely a primary battery) is discarded after use not only increases the cost, but also causes environmental pollutions. Therefore, a rechargeable battery (namely a secondary battery) has a higher demands than that of a primary battery since a rechargeable battery can save costs and reduce contaminations of waste batteries.
At present, rechargeable batteries include lithium-ion (Li-ion) batteries, nickel metal hydride (Ni-MH) batteries, nickel cadmium (Ni—Cd) batteries and the rechargeable alkaline batteries, and these batteries are also known as secondary batteries. Recently, a lithium battery with an organic electrolytic unit is used extensively in portable electronic devices due to its features of high-energy density, low temperature, and stable storage.
However, a lithium battery still has the following drawbacks in its use:
1. A lithium battery usually comes with different specifications for the electronic products from different brands. Even for the electronic products of the same brand, such as the Nokia mobile phones, there may be tens of models of the lithium batteries, and thus causing tremendous inconveniences and trouble to users.
2. A lithium battery contains an electrolytic unit, and there is a safety concern such as possible explosion when a over-current occurs.
3. Most of the present portable powers use a built-in lithium battery as an energy storage unit, but it generally does not come with a standard size for general electronic consumer products. As a result, the fully charged battery cannot be used alone when it is taken out. Even though it can be taken out, there are so many specifications of the lithium batteries, and such application is impractical.
Compared with the lithium battery, although the secondary battery, such as the nickel metal hydride (Ni-MH), nickel cadmium (Ni—Cd) or alkaline rechargeable secondary battery has an energy storage density less than that of the lithium battery, yet its widely used AA or AAA battery sets an industrial specification, which is the main reason of its popularity up to now. However, its use still has the following insufficiencies:
1. Although the AA or AAA battery charger has the charging and discharging functions, several pieces of batteries are usually connected in series and put into the charging compartment, and the same charging circuit is used for charging each battery. This application may have drawbacks such as overheating, leak and undercharge.
2. After the batteries (generally four pieces of batteries) in the charging compartment are fully charged by a conventional AA or AAA battery charger, it is necessary to connect the batteries in series in order to discharge a DC voltage equal to (1.2V˜1.5V)×4=4.8V˜6V for the use by portable electronic products, since each battery has a voltage approximately equal to 1.2V˜1.5V only. The conventional serially-connected batteries discharge electric power by turning ON/OFF an electronic switch or a relay composed of a semi-conducting unit, and positive and negative terminals of the batteries are serially connected to jointly discharge and supply electric power for the use as a charging power. However, the electronic switch has internal impedance when discharging a large current, and consumes energy during its ON/OFF operations. Furthermore, the voltage and current usually come with a phase difference, and thus there is a switching loss or a surge produced, and these factors affect the discharging performance and the energy storage of the charger when it is used as a discharger. Therefore, the electronic switch used as a switch component for the serially connected batteries is not a good option, and definitely requires further improvements. Thus, the inventor of the present invention has been devoted to the research and development of improving battery chargers/dischargers to overcome the above-mentioned drawbacks.